1. Field of the Invention
The present invention relates generally to a method of producing high-grade wood products, and, more specifically to a method of creating high-grade wood products from low-grade wood.
2. Description of the State of the Art
Lumber produced in sawmills is sorted into various lumber grades. In the case of a stud mill, lumber is sorted into high-grade (stud grade) lumber and low-grade lumber. Wood products are relegated to low-grade categories because of naturally occurring defects that decrease lumber strength characteristics, and thus prohibit its use for high-grade structural applications. Economy grade is the lowest grade of lumber and at most makes up to about twenty percent of the lumber recovered from a typical sawmill. Low-grade lumber is used primarily in non-structural applications such as pallets and shipping dunnage (material used to fill voids for shipping products).
Typical defects found in economy lumber include wane, pockets, shake, skip, voids, and splits. Wane is the bark, or the lack of wood from any cause, on the edge or corner of a piece of lumber. A waney edge is the natural wavy edge of a plank, which may still be covered by tree bark. A pocket is a well-defined opening between the rings of annual growth which develops during the growth of a tree. It usually contains pitch or bark. A shake is a separation along the grain between growth rings, or a break through the rings, usually the result of high winds. Skip is an area on a piece of lumber that a planer fails to surface, classified for grading purposes as slight, shallow or small, and deep or heavy. A void is an opening in the surface of the lumber. A split is a separation of the wood through the piece to the opposite surface.
Economy grade lumber can also have warp defects, including twist, bow, crook, sweep or any combination thereof. Twist is a warp defect in a board in which the board tends to assume the configuration of a portion of a spiral. In lumber with bow, the edges of the board lie on parallel planes but the faces are curved, much like a rocker of a rocking chair. Crook is deviation from linearity of the edges of a piece of lumber when it is laid on one of its widest faces and is warpage 90xc2x0 displaced from bow. A piece of lumber having only crook will have the faces lying in parallel plane with the edges curved. Sweep is longitudinal curvature along the tree, that is, sweep is the deviation from a straight line of the concave edge when the log is allowed to assume its natural position on a flat surface.
In a typical sawmill operation, logs are first sorted both in the woods and at the mill prior to processing. The next step is to de-bark useable logs and then process them through a primary breakdown such as a single bandsaw or a multiple bandsaw. This results in rectangular timbers known as xe2x80x9ccantsxe2x80x9d that vary in size according to the initial log dimensions. Generally, a cant is a large piece of lumber destined for further processing by other saws. The cants are then processed through a gang saw that cuts the cant in one pass into individual studs. A re-saw cuts the cant longitudinally into two additional rectangular pieces, typically half the width of the original cant. The pieces of wood that result from resawing a cant through the narrow face are referred to as xe2x80x9cflitchesxe2x80x9d. The flitches are then processed through an edger that cuts studs in one pass. The studs are then stacked and processed though a kiln to dry the lumber to a suitable moisture content of nineteen percent or less. The drying process will always down-grade some studs by generating stresses that cause warp defects in the stud. The dry studs are then processed through a planer that puts a smooth finish on the surfaces of the studs.
After planing and drying, each stud is visually graded by certified graders. The graders evaluate all defects according to grade rules, such as rules formulated by Western Wood Products Association (WWPA) for lumber manufacturers. Studs that do not meet stud grade requirement, such as those that are twisted, warped, bowed, contain large knots, excessive wane, splits or other defects, are downgraded either to utility or economy grade. Stud grade is intended for use in wall construction in homes and is required to have the strength needed to support walls and roof loads.
Different species of wood yield different percentages of each grade of lumber. Typically, Ponderosa Pine will yield fifty five percent stud grade lumber and twenty five percent economy grade lumber. Lodgepole pine, Spruce, and Douglas Fir typically yield eighty percent stud grade lumber and fifteen percent economy grade lumber. The remaining percentage in each species results in utility grade lumber. Currently, most trees that can be identified as containing mostly low-grade lumber are not sawn, but rather remain in the woods as waste, are harvested and sold for firewood, or chipped as pulp. This causes a tremendous waste of resources, since an estimated additional ten percent of fiber could be salvaged from every acre of forest harvested if there was an economical use for this low-grade material.
The economy grade lumber from logs that are currently processed as described above is typically either chipped as pulp or is sold and then re-processed as finger joint blocks, pallets, or used as dunnage. Presently, the only method to upgrade the low-grade material into a structural product is to selectively cut out the defects and finger joint the remaining pieces together to produce finger jointed structural lumber. While the cut-up process can be effective in recovering usable blocks from economy grade studs, it is generally cost effective only when at least half of the piece is recovered. However, less than ten percent of economy grade lumber is suitable for the finger joint application. Hence, a significant portion of lumber is lost to low-grade applications, thus increasing overall sawmill costs, and increasing demand for quality studs. Other than a small percentage (about ten percent) used for finger jointing blocks, no effective method has been developed to process this type of lumber to a higher value product.
Until a few years ago, there was no pressing need for sawmills to consider using low-grade wood. Unprocessed saw logs were plentiful, and sawmills could afford to waste poorer logs because they were relatively abundant and the price of timber was relatively low. Currently, however, the available old growth forests the once provided sawn lumber in standard dimensions for construction material are diminishing rapidly. Therefore, most of the lumber produced today is from much smaller trees obtained from second growth forests. Second growth trees are much smaller, and therefore it is increasingly difficult to produce lumber in the sizes and lengths obtained from the older trees. In addition, a higher percentage of xe2x80x9cwastexe2x80x9d, or unusable wood is produced in converting the second growth trees into lumber. An additional problem with second growth trees is that the physical geometry of the trees (i.e., twist, warp, bow) also contributes to the waste in producing straight lumber, since current methods generally comprise planing the wood to remove warpage, etc.
Current methods of producing laminated products involve the use of higher grade lumber that does not have defects such as twist, bow, crook or sweep from higher grade wood by various methods such as planing, cutting and/or pressing the wood prior to bonding pieces of lumber to make the laminated product. However, these current laminating methods have not been successful in utilizing economy grade lumber which has large knots, skips, pockets, warp, etc. This is due to the fact that economy grade lumber is either too warped to be resawn or falls apart if sawn prior to laminating due to the large knots in the lumber. Therefore, prior to the present invention, no process has been available to economically use low-grade material to create higher grade wood products.
Accordingly, it is a general object of this invention to provide a process by which low-grade lumber, (i.e., lumber containing defects such as wane, voids, skips, knots, splits, bark pockets, warp, etc.), is converted to higher grade lumber products. More specifically, the present invention provides a method by which economy grade lumber is converted to stud grade or higher grade lumber products.
It is another object of this invention to provide a method by which low-grade lumber having warp, twist, bow, knots, pockets, and other defects is converted to stud grade or higher grade lumber of various dimensions.
It is a further object of this invention to provide a method for preparing cants from low-grade lumber obtained from the same or from different species of trees for sawing into lumber of stud-grade or higher quality.
It is a further object of the invention to provide a high-grade laminated stud suitable for use as construction material.
It is a further object of the invention to provide a method wherein a higher percentage of low-grade wood material is converted into useful products suitable for construction material.
Additional objects, advantages, and novel features of the invention shall be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by the practice of the invention. The objects and the advantages may be realized and attained by means of the instrumentalities and in combinations particularly pointed out in the appended claims. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various change and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the foregoing and other objects and in accordance with the purposes and objects of the present invention, as embodied and broadly described herein, the method of the invention comprises (i) categorizing low-grade studs, (ii) arranging a plurality of categorized low-grade studs side by side in a specific manner such that surface defects such as knots or voids on adjacent studs are offset by a specified minimum distance and such that warp defects are counteracted, (iii) face-laminating the studs together to form a cant, and (iv) resawing the cant to yield laminated products which are classified as stud grade or higher. During the laminating process, warp defects may be removed from the cant by counteracting these defects in adjacent studs and applying pressure to the cant. The resulting laminated products are free of bowing or twisting, and have an acceptable amount of surface defects relative to the size of the final product, thus increasing the quality rating of the final laminated product relative to the original low-grade studs.